A wide range of growth factors coordinate cell proliferation and differentiation. Malignant cells arise as a result of a stepwise progression of events that include the unregulated expression of growth factors or components of their signaling pathways. Tyrosine phosphorylation events initiated by receptor, cytoplasmic and nuclear kinases and regulated by phosphatases are central to these processes. Mutation, hyper-activation, translocation and overexpression of protein tyrosine kinases are all associated with tumorigenesis. In addition to increasing proliferative rates and immortalizing cells, overexpression of tyrosine kinases can lead to morphological transformation and cause anchorage independence, contributing to the promotion of migratory ability and possibly the induction of metastases.
Certain compounds with structures based upon mimicry of ATP or phosphotyrosine have been shown to be effective kinase inhibitors. Those based upon phosphotyrosine have been demonstrated to be the more specific tyrosine kinase inhibitors. Because of their ability to inhibit tyrosine phosphorylation, these compounds may alter cell responses to growth factors or other process driven by tyrosine kinase activity, including unregulated growth as the result of tyrosine kinase overexpression, mutation, or translocation. Inhibition of tyrosine kinases occupying a central role in proliferative signaling pathways, or in pathways regulating cell cytoskeletal structure, even temporary or incomplete inhibition, may be sufficient to switch a cancerous cell from a proliferative cycle into programmed cell death, or apoptosis. Death by apoptosis is most often observed upon effective treatment with tyrosine kinase inhibitors.
Selective inhibition of specific tyrosine kinases offers a method of targeting cancerous cell growth with a high degree of specificity and minimal toxicity to normally growing cells and tissues. Thus, specific inhibitors of tyrosine kinases have great potential as clinical anti-cancer treatments. A number of small molecules which act as tyrosine kinase inhibitors have been identified. For example, certain phenyl acrylonitrile compounds have been described as tyrosine kinase inhibitors, effective to inhibit cell proliferation (see for example, U.S. Pat. Nos. 5,891,917, 5,217,999, 5,773,476, 5,935,993, 5,656,655, 5,677,329 and 5,789,427).
Inhibition of tyrosine kinases offers one mechanism by which cell proliferation can be inhibited. One of skill in the art will appreciate that other mechanisms of inhibition may also be involved.
There is a need in the art to identify compounds that inhibit cell proliferation.